The Relationship of the Tetracoralla to the Hexacoralla. 179 



tic of Tetracoralla. The calices are rarely preserved, for in ten 

 specimens examined only one showed the distal septal ends but 

 this one showed very clearly a division into quadrants. This 

 specimen is shown on PL I, Fig. 7. The septal arrangement is 

 indicated clearly in only one quadrant because of injuries to 

 the polyp which affected all except that region of the calyx. 

 A section made of one of the smaller specimens (PL I, Fig. 8) 

 also shows a division into quadrants as well as the typical 

 quadriseptal arrangement. It is noteworthy that the external 

 ridges of this corallite do not alternate with the septa but are 

 opposite the external septal ends. 



Specimens of Hexaphyllia m'coyi (Heterophyllia Duncan) 

 from the Scottish Lower Limestone Group at Gilnockie near 

 Canonbie, Scotland, correspond closely to those described by 

 Stuckenberg. Their mode of attachment is unknown as the 

 fossils invariably occur as bix)ken sections of the prismatic coral- 

 lum. These sections vary from less than i mm. to 2 mm. in 

 diameter. Neumayr (1889 B:2yy) suggested that these six- 

 septal forms were related to the large individuals of Hetero- 

 phyllia in a way similar to that in dimorphic individuals of 

 Battersbyia. 



Duncan, however (1867:645, 646), made separate species for 

 the six-septal forms. He divided the genus Heterophyllia into 

 two groups, one containing large forms with many septa, and one 

 including small corallites with six septa. Eight species were 

 described by him, three of them being forms with only six 

 septa, — H. m'coyi, H. lyelli, and H. mirabilis. The genus was 

 redefined by Duncan as follows: 



"The corallum is simple, long, and slender. The gemmation 

 takes place around the calicular margin, and is extracalicular. 

 The septa are either irregular in number and arrangement, or 

 else are six in number and regularly spaced. The costse are well 

 developed, and may be tubercular, spined, and flexuous. The 

 wall is thick, there is no epitheca and the endotheca is dis- 

 sepimental." 



Another form so closely related to the three six-septal species 

 of Heterophyllia that it must be placed in the same genus, was 

 found by Stuckenberg (1904) in central Russia. Upon this 

 species, H. prismatica, he based a new genus Hexaphyllia which, 

 he indicated, should also contain the six-septal forms of Hetero- 



